14 DAY TRIAL // Ubuntu MATE usually incorporates the latest version of the MATE desktop environment at launch, but the packages get updated before a new version of the OS is released. It's possible to upgrade the desktop environment with the latest packages, at your own risk.
One of the things that developers do over and over again is to test the OS after they made a serious change to it. When you upgrade the desktop environment, you make a big change on your systems and it's only normal to face a small risk for things to go wrong. It's not likely, but any upgrade to the OS that's not officially supported is not advisable.
With that in mind, users need to know that there are a couple of PPAs available out there that allow users to install newer versions of the MATE desktop on Ubuntu MATE. This is done fairly easily, and the PPAs are not from third-party devs. They should be safe enough to use, but please remember what I said above about upgrading the desktop environment or any other critical components.
How to install the latest MATE in Ubuntu MATE
The MATE desktop environment is now at version 1.12.1, and that particular version is already available in the PPAs. These are different repositories for both the 15.10 and 16.04 branches. There is only one caveat. The latest stable version is 15.10, and 16.04 is still under development.
If you're using the early Ubuntu MATE 16.04 build, there is no telling what kind of conflict there will be between the MATA PPA and the changes pushed by the developers via the regular channels.
Installation is easy, just enter these commands in a terminal near you:
Ubuntu MATE 15.10
sudo apt-get update
sudo apt-get dist-upgrade
Ubuntu MATE 16.04
sudo apt-get update
sudo apt-get dist-upgrade